Habitat, Sexual and Allometric Influences on Morphological Traits of Intertidal Crabs

Abstract

Intertidal crabs display distinct morphological traits that allow differential interactions with biotic and abiotic features of the intertidal landscape, but are also influenced by allometry and sexual selection. This study aimed to explore the influence of sexual, allometric and habitat factors on morphological variation in the intertidal mangrove crab assemblage. A standardized photographic protocol was developed using readily available, low-cost technology to capture the morphology of carapaces and claws as sets of Cartesian landmarks. Digitization errors were 1 to 2 orders of magnitude smaller than the variation among individuals. In Tubuca seismella and Tubuca signata (superfamily Ocypodoidea), species that have traditionally been studied for sexual dimorphism, standardized major claw sizes were 2.8 and 3.7, respectively, times larger for males than females. Sexual dimorphism in claw size was also observed for Metopograpsus frontalis and Parasesarma longicristatum (superfamily Grapsoidea), with the largest claw in males being 15% and 33%, respectively, larger than in females. In contrast to size, claw shape did not relate to sex, except for T. seismella. Carapace shape, although variable among individuals and displaying asymmetry, was unrelated to sex. Claw and carapace shapes displayed high correlations, with values around 0.78. Carapace shapes grouped into taxonomic families and linked to habitat preferences, while claw shapes varied along a taxonomic gradient. These results complement studies on crab morphology that focus on specific factors or species, and stress the importance of multiple, interacting factors including sexual, allometric and habitat influences as drivers of morphological trait variability.

Phylomorphometrics reveal ecomorphological convergence in pea crab carapace shapes (Brachyura, Pinnotheridae)

“…Firm homologous structures like skeletons seem to be easier to compare, but soft‐bodied invertebrate taxa pose a problem in this respect. Invertebrates like mollusk bivalves or gastropods have, however, been studied thanks to their hard (partial) exoskeleton (Burridge et al, 2015 ; Potkamp et al, 2017 ; Sherratt et al, 2016 ; Verhaegen et al, 2018 ), but for unknown reasons, crustaceans seem to be underrepresented in the field of eco‐, and phylomorphometrics (with the exception of Marochi & Masunari, 2016 ; Trontelj et al, 2012 ; Vermeiren et al, 2021 ).…”

Quantitative Comparison of Avian and Mammalian Physiologies for Parameterization of Physiologically Based Kinetic Models

“…In homothermic vertebrates, allometric relationships exist not only for metabolic rate but also for organ weights [e.g., negative for heart mass in birds: Grubb (1983) and African mammals (reviewed: Smith, 1984 ) and positive for skeletal mass in mammals and birds: Prange et al (1979) ], development ( Cooney et al, 2020 ), pharmacokinetics ( Knibbe et al, 2005 ) and calculating drug dosages for laboratory animals ( Lindstedt and Schaeffer, 2002 ). In addition, allometric relationships have been reported in invertebrate species; there being, for instance, such relationships for size or weight of the stomach ( Griffen et al, 2018 ) and claws ( Vermeiren et al, 2020 ) in crabs and multiple organs in coleopteran and hymenopteran insects ( Polilova and Makarova, 2017 ).…”

Ecomorphological aspects in the evolution of endosymbiotic crustaceans

“…Firm homologous structures like skeletons seem to be easier to compare, but soft-bodied invertebrate taxa pose a problem in this respect. Invertebrates like mollusk bivalves or gastropods have, however, been studied thanks to their hard (partial) exoskeleton (Burridge et al, 2015;Sherratt et al, 2016;Verhaegen et al, 2018), but for unknown reasons, crustaceans seem to be underrepresented in the field of eco-, and phylomorphometrics (with the exception of Marochi & Masunari, 2016;Trontelj et al, 2012;Vermeiren et al, 2021).…”